While it may be a reaction to the epoxy, I would be just as worried about fine particulate matter. Are there fiberglass (or wood) particles in the air? Not just when you are working, but when you are just standing around thinking what to do next. Wood can cause an allergic reaction, and if that is the case a change to a different species might alleviate the problem. Fiberglass particles may cause a reaction in your lungs and nostrils. In any cast clean air is very important.